well, aluminum is different from silver. Investiture can still do stuff with it (you can soulcast aluminum, its just harder) and it has been theorized that you cannot tap aluminum (aluminum is feruchemical identity). Hemalurgic Aluminum makes sense, because what does aluminum mainly do? It cuts of investiture connection. Its like an investiture insulator. So, if you were to stick that insulator, that blocker, into someone's spiritweb, they wouldn'gt be able to acces/utilize it. And, aluminum clearing your metals makes sense, you give it some energy, and it just blocks off the energy from accessing the rest.
Forgive my rant, and all my spelling errors, I just am interested in scadrial and know a lot about metals and aluminum